Antioxidant Activities and Oxidative Stabilities of Some Unconventional Oilseeds

The oils of some unconventional oilseeds (hemp, radish, terebinth, stinging nettle, laurel) were obtained by a cold-press method in which the total oil content, fatty acids, tocopherol isomers, some metal contents (Ca, Mg, Fe, Cu), antioxidant activity and oxidative stability were determined. The total oil content was determined ranging between 30.68 and 43.12%, and the oil samples had large amounts of unsaturated fatty acids, with oleic acid and linoleic acid. Of all the oils, terebinth seed oil had the highest α-tocopherol content (102.21 ± 1.01 mg/kg oil). Laurel oilseed had the highest antiradical activity in both the DPPH and ABTS assays. The peroxide value of the non-oxidized oils ranged between 0.51 and 3.73 mequiv O₂/kg oil. The TBARS value of the non-oxidized oils ranged between 0.68 ± 0.02 and 6.43 ± 0.48 mmol MA equiv/g oil. At 110 °C, the Rancimat induction period of the oils ranged between 1.32 and 43.44 h. The infrared spectra of the samples were recorded by FTIR spectroscopy. The absorbance values of the spectrum bands were observed and it was determined that some of the chemical groups of oxidized oils caused changes in absorbance. As a result of the present research, the analyzed oils could be evaluated as an alternative to traditionally consumed vegetable oils or as additives to them.     

Oxidative Stability of Chia (<Emphasis Type="Italic">Salvia hispanica</Emphasis> L.) Seed Oil: Effect of Antioxidants and Storage Conditions

The oxidative stability of chia oil was evaluated by measuring the effectiveness of the addition of rosemary (ROS) and green tea (GT) extracts, tocopherols (TOC), ascorbyl palmitate (AP) and their blends, and studying the influence of storage conditions. The addition of antioxidants increased induction time, depending on their type and concentration. Considering antioxidants individually, AP at 5,000 ppm was the most effective, whereas ROS + GT at 2,500 and 5,000 ppm provided the best protection among the antioxidant blends. Chia oil peroxide values of 10 mequiv/kg was observed for oils stored at 4 °C while values greater than 10 mequiv/kg were observed between 60 and 120 days when stored at 20 °C. Only AP 2,500 ppm protected oil did not reach 10 mequiv/kg during 225 days at 4 and 20 °C. Similar trends were observed with p-anisidine and Totox values. Differential scanning calorimetry further supported the presence of primary and secondary oxidation. Activation energy of chia oil thermoxidation was 71.9 kJ/mol increasing up to 87.5 kJ/mol when AP was added.     

Evaluation of the Oxidative Stability of Diacylglycerol-Enriched Soybean Oil and Palm Olein Under Rancimat-Accelerated Oxidation Conditions

The oxidative stability of diacylglycerol (DAG)-enriched soybean oil and palm olein produced by partial hydrolysis using phospholipase A1 (Lecitase Ultra) and molecular distillation was investigated at 110 °C by the Rancimat method with and without addition of synthetic antioxidants. Compared with triacylglycerol oils, the DAG-enriched oils displayed lower oxidative stability due to a higher content of unsaturated fatty acids and a lower level of tocopherols. With the addition (50–200 mg/kg) of tert-butylhydroquinone (TBHQ) or ascorbyl palmitate (AP), the oxidative stability indicated by induction period (IP) of these DAG-enriched oils under the Rancimat conditions was improved. The IP of the diacylglycerol-enriched soybean oil increased from 4.21 ± 0.09 to 12.64 ± 0.42 h when 200 mg/kg of TBHQ was added, whereas the IP of the diacylglycerol-enriched palm olein increased from 5.35 ± 0.21 to 16.24 ± 0.55 h when the same level of AP was added. Addition of TBHQ, alone and in combination with AP resulted in a significant (p ≤ 0.05) increase in oxidative stability of diacylglycerol-enriched soybean oil. AP had a positive synergistic effect when used with TBHQ.     

Changes in Total Polar Compounds,Peroxide Value,Total Phenols and Antioxidant Activity of Various Oils Used in Deep Fat Frying

In this study, the effect of deep fat frying on oil degradation, total phenols (TP) and total antioxidant activity (TAA) of hazelnut, corn, soybean and olive oils were investigated. Oil degradation and oxidation were monitored by measuring the total polar compounds (TPC) and the peroxide value (PV). The amount of TPC in corn, soybean and olive oils increased significantly with the time increment (p < 0.05). The PV of the oils did not exceed the maximum acceptable limit of 10 mequiv O₂/kg after 125 min frying except for hazelnut oil (10.64 mequiv O₂/kg). Deep-fat frying did not cause any significant change in the TP of corn oil, soybean oil and olive oil (p < 0.05). A significant decrease in the antioxidant activity was observed after 50 min frying using hazelnut oil and corn oil (p < 0.05). However, the antioxidant activity of soybean oil and olive oil significantly decreased after 75 and 25 min frying, respectively.     

Effect of Dehulling Treatment on the Oxidative Stability of Cold-Pressed Low Erucic Acid Rapeseed Oil

This study compared the oxidative stability of cold-pressed rapeseed oil (CPRO) and dehulled cold-pressed rapeseed oil (DCPRO) in the dark at 60 °C and monitored the evolution of minor constituents (tocopherols, phytosterols, phenolics). The results showed that dehulling significantly influenced the oxidative stability of the oils, the DCPRO was more easily oxidized. During the autoxidation, the peroxide value (PV) and anisidine value (p-AV) of the DCPRO ranged from 2.38 to 95.97 mequiv O₂ kg⁻¹ and from 1.20 to 30.75, whereas those of the CPRO ranged from 3.80 to 46.17 mequiv O₂ kg⁻¹and from 2.69 to 14.87, respectively. Dehulling affected the contents and the rates of decrease of tocopherols and phytosterols of the cold-pressed oils, and the rates of decrease of tocopherols and phytosterols of the CPRO were lower than those of the DCPRO (10% less, on average). The rancimat induction periods (IPs) were positively correlated with the concentrations of the total tocopherols (For DCPRO, R ² = 0.9622, For CPRO, R ² = 0.8334). The total phenolics contents as determined by spectrophotometry first increased and then decreased. Tocopherols and phytosterols had a greater effect on oxidative stability of the rapeseed oils during the first 30 days, and phenolics had a greater effect in the 30–40 day period.     

Effect of Temperature and Time on the Stability of Salmon Skin Oil During Storage

The effect of 45 days of storage at 25, 4, −18 and −80 °C on the quality indices; free fatty acid (FFA) content, peroxide value (PV), thiobarbituric acid reactive substances (TBARS), and changes in the fatty acid (FA) profile of crude oil recovered from salmon fish skins were evaluated at 5 day intervals using spectrophotometric and titrimetric methods. Higher temperatures and longer storage time resulted in higher quantities of oxidative products in the salmon skin oil (SSO). By day 45, SSO stored at 25 and 4 °C had 8.50 and 8.29% FFA, 32.43 and 26.33 μg malondialdehyde (MDA) eq g⁻¹ oil, and 88.19 and 64.53 mequiv peroxide kg⁻¹ oil, respectively. No significant (p > 0.05) changes in fatty acid profile were observed at all the storage temperature and time studied.     

Oxidative Stability of Polyunsaturated Edible Oils Mixed With Microcrystalline Cellulose

The oxidative stability of mixtures of edible oils containing polyunsaturated fatty acids (PUFA) and microcrystalline cellulose (MCC) was investigated. The mixtures studied consisted of oils of either camelina (CAM), cod liver (CLO), or salmon (SO) mixed with either colloidal or powdered MCC. A 50:50 (w/w) ratio of oil:MCC resulted in an applicable mixture containing high levels of PUFA edible oil and dietary fiber. The oxidative stability of the formulated mixtures and the pure oils was investigated over a period of 28 days. The peroxide value (PV) was assessed as a parameter for primary oxidation products and dynamic headspace gas chromatography mass spectrometry (GC/MS) was used to analyze secondary volatile organic compounds (VOC). CAM and the respective mixtures were oxidatively stable at both 4 and 22 °C during the storage period. The marine oils and the respective mixtures were stable at 4 °C. At 22 °C, an increase in hydroperoxides was found, but no increase in VOC was detected during the time-frame investigated. At 42 °C, prominent increases in PV and VOC were found for all oils and mixtures. Hexanal, a common marker for the degradation of n-6 fatty acids, propanal and 2,4-heptadienal (E,E), common indicators for the degradation of n-3 fatty acids, were among the volatiles detected in the headspace of oils and mixtures. This study showed that a mixture containing a 50:50 ratio of oil:MCC can be obtained by a low-tech procedure that does not induce oxidation when stored at low temperatures during a period of 1 month.     

Effect of Storage Conditions and Antioxidants on the Oxidative Stability of Sunflower–Chia Oil Blends

The mixture of different proportions of sunflower with chia oil provides a simple method to prepare edible oils with a wide range of desired fatty acid compositions. Sunflower–chia (90:10 and 80:20 wt/wt) oil blends with the addition of rosemary (ROS), ascorbyl palmitate (AP) and their blends (AP:ROS) were formulated to evaluate the oxidative stability during storage at two temperature levels normally used, cool (4 ± 1 °C) and room temperature (20 ± 2 °C) for a period of 360 days. Peroxide values (PV) of the oil blends with antioxidants stored at 4 ± 1 °C showed levels ≤10.0 mequiv O₂/kg oil; the lowest levels of PV were found for blends with AP:ROS. Values higher than 10.0 mequiv O₂/kg were observed between 120–240 days for oil blends stored at 20 ± 2 °C. Similar trends were observed with p-anisidine and Totox values. The oxidative stability determined by the Rancimat method and differential scanning calorimetry showed a greater susceptibility of the oils to oxidative deterioration with increasing unsaturated fatty acids content. The addition of antioxidants increased the induction time and decreased the Arrhenius rate constant, indicating an improvement in the oxidative stability for all the oil blends. Temperature had a strong influence on the stability of these blends during storage.     

Oxidation of Corn Oils with Spiked Tocols

Stripped corn oils with added tocopherols and tocotrienols, at concentrations between 100 and 5,000 ppm, were used to evaluate antioxidant activity of these tocol compounds. The formation of lipid hydroperoxides, measured as peroxide value (PV), was accelerated at 60 °C in the dark for 5 days. Resistance to oxidation as induction period (IP) was also measured using an oxidative stability instrument (OSI) at 100 °C. For PV inhibition, the oils containing α-tocols exhibited decreasing effectiveness with increasing concentration. At day five, samples with 100 ppm α-tocols had the lowest PVs of about 40 mequiv/kg and samples containing 5,000 ppm had the highest values, ranging from 150 to 200 mequiv/kg. At concentrations above 700 ppm of α-tocols, there was an inversion of antioxidative properties as α-tocols promoted lipid oxidation. The opposite concentration effect was observed with δ-tocols and γ-tocotrienol (T3) for which antioxidant effectiveness increased with concentration. OSI-IP hour at 100 °C increased with increasing tocol concentrations for all tocol homologs, although with diminishing effectiveness at greater than 700 ppm. The α-tocols were less effective in extending the IP (~9 h at 5,000 ppm) than the δ-tocols and γ-T3 (13–14 h at 5,000 ppm). Therefore, the antioxidant or prooxidant activities of different tocols are different and the outcomes are different depending on the evaluation methods used.     

Oxidative instability of CLA concentrate and its avoidance with antioxidants

This study evaluated the effectiveness of antioxidants, such as BHA, BHT, TBHQ, propyl gallate (PG), α-tocopherol (α-1), green tea extract (GTE), and rosemary extract (RE) on oxidative stability of CLA concentrate. Stability of CLA concentrate stored in air at 45°C up to 44 d was assessed by PV. During the storage period, the PV of the control CLA concentrate sample increased from 0.20 (fresh oil) to 1654 meq/kg (oxidized oil). On the other hand, the PV for CLA concentrates treated with 200 ppm of the single synthetic antioxidants, BHA, BHT, TBHQ, and PG, increased from 0.20 to 81, 107, 78, and 101 meq/kg, respectively. Also, the PV of CLA concentrate with the addition of 200 ppm single natural antioxidants α-T, GTE, and RE lowered the final PV to 122, 140, and 110 meq/kg, respectively. Under our experimental conditions, the protective effect of 200 ppm antioxidant was in the order of TBHQ>BHA>PG>BHT>RE>α-T> GTE. These results suggest that the appropriate use of antioxidants prolongs the oxidative stability of CLA concentrate.     

Body Compositional Changes and Growth Alteration in Chicks from Hens Fed Conjugated Linoleic Acid

Effects of feeding conjugated linoleic acid (CLA) to hens on progeny chick development and composition at hatch (NHC) and three weeks of age (TWC) were assessed. CLA (0 or 0.5%, composed of mixed isomers of cis-9,trans-11 or trans-10,cis-12-CLA) was fed to hens with either safflower (SO) or olive oil (OO) (3 or 3.5%) to assure successful hatch for 2 weeks prior to collection for incubation. Maternal CLA feeding had no effect on hatchability, but improved egg fertility (p < 0.05). Maternal feeding of CLA with SO increased 21 day-old progeny growth, while CLA with OO decreased growth (oil*CLA, p < 0.05). In 25 day-old chicks (TWC), but not NHC, maternal CLA decreased the proportion of total body water (p < 0.05) and increased body ash (p < 0.05). While monounsaturated fatty acids were decreased and saturated fatty acids increased in eggs and NHC from hens fed CLA, no differences in fatty acid composition were observed in chicks at 25 days of age from hens fed CLA. Maternal CLA feeding resulted in the presence of c9,t11 and t10,c12-CLA in NHC, but only c9,t11 in the TWC. In conclusion, hens fed CLA led to improved fertility and altered body composition at 3 weeks of age.     

Quantitative determination of total lipid hydroperoxides by a flow injection analysis system

A flow injection analysis (FIA) system coupled with a fluorescence detection system using diphenyl-1-pyrenylphosphine (DPPP) was developed as a highly sensitive and reproducible quantitative method of total lipid hydroperoxide analysis. Fluorescence analysis of DPPP oxide generated by the reaction of lipid hydroperoxides with DPPP enabled a quantitative determination of the total amount of lipid hydroperoxides. Use of 1-myristoyl-2-(12-((7-nitro-2-1,3-benzoxadiazol-4-yl)amino) dodecanoyl)-sn-glycero-3-phosphocholine as the internal standard improved the sensitivity and reproducibility of the analysis. Several commercially available edible oils, including soybean oil, rapeseed oil, olive oil, corn oil, canola oil, safflower oil, mixed vegetable oils, cod liver oil, and sardine oil were analyzed by the FIA system for the quantitative determination of total lipid hydroperoxides. The minimal amounts of sample oils required were 50 μg of soybean oil (PV=2.71 meq/kg) and 3 mg of sardine oil (PV=0.38 meq/kg) for a single injection. Thus, sensitivity was sufficient for the detection of a small amount and/or low concentration of hydroperoxides in common edible oils. The recovery of sample oils for the FIA system ranged between 87.2±2.6% and 102±5.1% when PV ranged between 0.38 and 58.8 meq/kg. The CV in the analyses of soybean oil (PV=3.25 meq/kg), cod liver oil (PV=6.71 meq/kg), rapeseed oil (PV=12.3 meq/kg), and sardine oil (PV=63.8 meq/kg) were 4.31, 5.66, 8.27, and 11.2%, respectively, demonstrating sufficient reproducibility of the FIA system for the determination of lipid hydroperoxides. The squared correlation (r ²) between the FIA system and the official AOCS iodometric titration method in a linear regression analysis was estimated at 0.9976 within the range of 0.35−77.8 meq/kg of PV (n=42). Thus, the FIA system provided satisfactory detection limits, recovery, and reproducibility. The FIA system was further applied to evaluate changes in the total amounts of lipid hydroperoxides in fish muscle stored on ice.     

Brazilian encapsulated fish oils: Oxidative stability and fatty acid composition

Encapsulated fish oils are extensively commercialized in Brazil. These products could have an effect in the reduction of heart diseases because of their high content of polyunsaturated fatty acids. However, information about their composition and quality are still lacking. Fatty acid composition, oxidative stability (Rancimat, 80°C, 2.5 g sample and 8.3 L/h air), peroxide value (PV), and polar compound content were determined in sixteen trademarked encapsulated fish and cod-liver oils, purchased from Brazilian markets. The highly polyunsaturated fatty acid (eicosapentaenoic acid+docosahexaenoic acid) level appear to be typical of marine oils (16.2 and 32.1%). The PV ranged from 2.1 to 20.3 meq/kg, which is considered high, whereas the Rancimat induction periods varied from 1.95 to 8.45 h. The samples analyzed contained from 0.1 to 8.3% polar components. In some cases, both composition and quality were inadequate for this kind of product. One of the samples did not contain cod-liver oil, it appears that it contained soybean oil. Presented at the 6th Latin American Congress and Exhibit on Fats and Oil Processing, LA-AOCS, Campinas, SP, Brazil, Sept. 1995.     

Aqueous Extraction and Enzymatic Destabilization of Coconut Milk Emulsions

Fresh and mature coconuts were subjected to deshelling, paring and disintegration. The coconut milk was extracted, treated with an enzyme (protease) at different concentrations and centrifuged, in order to separate it into coconut cream and aqueous phases. Subsequently, coconut cream was subjected to chilling (different temperatures) and thawing to ambient temperature (29 ± 2 °C) followed by centrifugation to obtain a clear virgin coconut oil (VCO). Coconut milk treated with aspartic protease at concentration of 0.02 mg/g, resulted in 90.4 ± 1.2% yield. A maximum yield of 95.3 ± 1.0% was obtained when the treatment of coconut milk with aspartic protease at concentration of 0.02 mg/g was followed by chilling (5 °C) and thawing. Physicochemical properties and fatty acid compositions were evaluated and compared with commercial coconut oil samples. It was found that the oil obtained from present study is low with respect to free fatty acids (0.31%) and peroxide value (0.81 mequiv O₂/kg) when compared with the commercial coconut oil samples. Sensory evaluation was also carried out to ensure the product acceptability.     

Chemical composition of commercial cornicabra virgin olive oil from 1995/96 and 1996/97 crops

The chemical composition of commercial Cornicabra virgin olive oils (n=65) was studied, as was its relationship with oil quality and the influence of the extraction method and production year. The main characteristics of these olive oils were: oxidative stability 53 ± 24 h, mean polyphenol content 162 ± 57 mg/kg (as gallic acid), oleic acid 80.8 ± 0.9%, linoleic acid 4.6 ± 0.6%, and campesterol 4.3 ± 0.1%, which is peculiar to this variety. No clear differences in composition were observed with respect to the different extraction systems (dual-phase/triple-phase decanters and pressure), although oils produced by the dual-phase decanter showed higher oxidative stability and polyphenol content. There were significant differences in major fatty acids and sterols according to the production year.     

Dietary Conjugated Linoleic Acid Induces Lipolysis in Adipose Tissue of Coconut Oil-Fed Mice but not Soy Oil-Fed Mice

Mice fed diets containing conjugated linoleic acid (CLA) are leaner than mice not fed CLA. This anti-obesity effect is amplified in mice fed coconut oil-containing or fat free diets, compared to soy oil diets. The present objective was to determine if CLA alters lipolysis in mice fed different base oils. Mice were fed diets containing soy oil (SO), coconut oil (CO), or fat free (FF) for 6 weeks, followed by 10 or 12 days of CLA or no CLA supplementation. Body fat, tissue weights, and ex vivo lipolysis were determined. Relative protein abundance and activation of perilipin, hormone sensitive lipase (HSL), adipose triglyceride lipase (ATGL), and adipose differentiation related protein (ADRP) were determined by western blotting. CLA feeding caused mice to have less (P < 0.05) body fat than non-CLA fed mice. This was enhanced in CO and FF-fed mice (CLA × oil source, P < 0.05). There was also a CLA × oil source interaction on lipolysis as CO + CLA and FF + CLA-fed mice had increased (P < 0.05) rates of lipolysis but SO + CLA-fed mice did not. However, after 12 days of CLA consumption, activated perilipin was increased (P < 0.05) only in SO + CLA-fed mice and total HSL and ATGL were decreased (P < 0.05) in CO + CLA-fed mice. Therefore, the enhanced CLA-induced body fat loss in CO and FF-fed mice appears to involve increased lipolysis but this effect may be decreasing by 12 days of CLA consumption.     

Effect of natural antioxidants in virgin olive oil on oxidative stability of refined,bleached, and deodorized olive oil

The factors influencing the oxidative stability of different commercial olive oils were evaluated. Comparisons were made of (i) the oxidative stability of commercial olive oils with that of a refined, bleached, and deodorized (RBD) olive oil, and (ii) the antioxidant activity of a mixture of phenolic compounds extracted from virgin olive oil with that of pure compounds andα-tocopherol added to RBD olive oil. The progress of oxidation at 60°C was followed by measuring both the formation (peroxide value, PV) and the decomposition (hexanal and volatiles) of hydroperoxides. The trends in antioxidant activity were different according to whether PV or hexanal were measured. Although the virgin olive oils contained higher levels of phenolic compounds than did the refined and RBD oils, their oxidative stability was significantly decreased by their high initial PV. Phenolic compounds extracted from virgin olive oils increased the oxidative stability of RBD olive oil. On the basis of PV, the phenol extract had the best antioxidant activity at 50 ppm, as gallic acid equivalents, but on the basis of hexanal formation, better antioxidant activity was observed at 100 and 200 ppm.α-Tocopherol behaved as a prooxidant at high concentrations (>250 ppm) on the basis of PV, but was more effective than the other antioxidants in inhibiting hexanal formation in RBD olive oil.o-Diphenols (caffeic acid) and, to a lesser extent, substitutedo-diphenols (ferulic and vanillic acids), showed better antioxidant activity than monophenols (p- ando-coumaric), based on both PV and hexanal formation. This study emphasizes the need to measure at least two oxidation parameters to better evaluate antioxidants and the oxidative stability of olive oils. The antioxidant effectiveness of phenolic compounds in virgin olive oils can be significantly diminished in oils if their initial PV are too high.     

Effect of Different Frying Methods on the Total <Emphasis Type="Italic">trans</Emphasis> Fatty Acid Content and Oxidative Stability of Oils

The main objective of this study was to determine the effect of different frying oils and frying methods on the formation of trans fatty acids and the oxidative stability of oils. Sunflower, canola and commercial frying oils, the most commonly used oils for frying potatoes in the fast food industry, were used as the frying medium. The value for total polar compounds was highest when commercial frying oil was used in the microwave oven (22.5 ± 1.1). The peroxide value, as an indicator of oil oxidation, was lowest for microwave oven frying (2.53 ± 0.03). The K₂₃₂ and K₂₇₀ values were 0.41 ± 0.04 and 0.18 ± 0.02, respectively, for commercial frying oil in the microwave oven. The lowest free fatty acid content was recorded for the commercial frying oil used in the deep‐fat fryer at 190 °C. The highest iodine value was measured for sunflower oil used in the deep‐fat fryer (148.14 ± 0.07), indicating a greater degree of unsaturation. The lowest trans fatty acid value was recorded for sunflower oil in the microwave oven (0.17 ± 0.05), with a higher overall amount of total trans fatty acids observed for oils after frying in the electrical deep‐fat fryer compared to the microwave. Sunflower oil was favourable for both frying methods in terms of the trans fatty acid content.